The invention relates to the transfer of files from a transmitting device to a receiving device in a digital telecommunication system in general and to a method of using a file mapping procedure mentioned but not strictly defined in the standard ETS 300 401 to transfer information associated with the files to be transferred.
Digital Audio Broadcasting (DAB) is a new transmission system, which is expected in the long run to replace the broadcasting systems based on analog amplitude and frequency modulation, which are presently used in radio broadcasting to masses of people. The main features of the definitions concerning the DAB system are presented in the standard ETS 300 401 of the European Broadcasting Union (EBU) and the European Telecommunications Standards Institute (ETSI). In order to shed light on the background of the present invention, the features of the DAB system which are essential with regard to the invention will be presented briefly in the following.
One signal stream transmitted by a transmitting device according to the standard forms a DAB ensemble, which can contain many services (2, 3, 4) as shown in FIG. 1. From the user""s point of view, each service corresponds to one radio channel of the present systems, and it consists of one or more service components 5, 6, 7, 8, 9, 10. A single service component 5 can contain, for example, the audio part offered by the service 2, such as music, or a data part associated with it, such as the lyrics of the song being played, or other information associated with the service 2. One service component 6 can be a part of more than one service 2, 4. The service component, which is the most essential with regard to the service is called the primary service component, and the other service components which belong to the service are called secondary service components. The primary service component is often the audio part offered by the service, but it can also be a data part. The service can also contain many audio parts as service components. FIG. 1 shows the connection between each service (such as Radio A; 2) and its primary service component (in this case Audio; 5) with a thick line.
The information to be transmitted over the radio interface of the DAB system from the transmitter to the receiver is divided into three channels according to its purpose, as shown in FIG. 2. The channels are: Main Service Channel (MSC) 11, Fast Information Channel (FIC) 12 and Synchronization Channel 13. The service components 5 to 10 mentioned above are transmitted in the service channel 11, which is further divided into separate convolution-coded sub-channels (11a, 11b, 11c, 11d, 11e in FIG. 1). Each sub-channel can transmit one or more service components. The mutual order of the service components and the sub-channels is called multiplex configuration. The fast information channel 12 contains the multiplex configuration information (MCI) in particular, but it can also be used to transmit other information quickly from the transmitter to the receiver. The synchronization channel 13 is used to control the transmission and reception operation of the system, such as the synchronization of the transmission frames.
A DAB transmission consists of parts that are positioned hierarchically. The uppermost level of hierarchy is the transmission frame 14 according to FIG. 2, which contains a separate portion for each of the three channels 11, 12, 13. Only the portion of the service channel 11 is essential with regard to the invention, and it will be described in more detail in the following.
The portion of the service channel of the transmission frame consists of Common Interleaved Frames (CIF) 15, of which there are one or four, depending on the type of the transmission frame 14, and each of which contains 55296 bits. Each common interleaved frame 15 can be further divided into Capacity Units (CU), not shown in the figure, of which there are 864, each with a length of 64 bits. The capacity units are in the common interleaved frame 15, numbered consecutively so that the number or address of the first capacity unit is 0 and that of the last one is 863. The relation of the above mentioned sub-channels to the capacity units is such that one subchannel comprises an integer number of consecutive capacity units. One capacity unit can belong to one sub-channel only. If the sub-channels do not use all the capacity units of the common interleaved frame 15, the remaining capacity units are filled with padding bits, which are zeros.
Two transport modes have been defined for the service channel 11, namely the stream mode and the packet mode. Because the invention relates only to the use of the packet mode, only that will be described in the following.
When information to be transmitted in the service channel is formed and processed in the transmission equipment, it is handled as so called logical frames. One logical frame contains the amount of information associated with one service component, the presentation of which to the user takes 24 milliseconds. The number of bits contained by it depends on at which point of the transmission coding the logical frame is handled, and what is the bit rate associated with the subchannel used to transmit it. The information contained by each logical frame is, in the case of the packet mode, further grouped into packets, an integer number of which are incorporated in the logical frame. The length of the packets is 24, 48, 72 or 96 bytes, or 192, 384, 576 or 768 bits. Each packet comprises a packet header, which includes, among other things, a 10-bit address indicating which service component the information contained by the packet is associated with. In addition, each packet comprises a data field and a checksum field. All packets containing information relating to the same service component have the same address. The above mentioned multiplex configuration information MCI transmitted by the fast information channel contain links by which the addresses of the packets are associated with the corresponding service components.
For transmission, the packets are arranged in a manner presented in the standard ETS 300 401 to the above mentioned sub-channels. Each sub-channel can contain packets, which have the same or a different address. Within the service channel, packets with different addresses can be transmitted in any order, but the mutual order of packets with the same address, which refer to the same service component, must be retained.
Information associated with the service components is related to the packets mentioned above in a manner such that data groups 16 according to FIG. 3 are formed thereof, and the data groups 16 are divided into parts for transmission, which parts are placed into packets 17, 18, 19, with the same address. It is for this reason that the mutual order of packets with the same address must be maintained: if the order is changed, the contents of the data group transmitted by the packets can no longer be reconstructed correctly. The first packet 17 transmitting the data group 16 contains an address (not shown) in its header 17a, which address is here denoted by j. Its header 17a also contains the information that it is the first packet of data group 17, which means that the so called First-bit of the header 17a is 1, and the so called Last-bit is 0. All the following packets 18, 19, which transmit the same data group 17, contain the same address j (not in the Figure) in their header 18a, 19a. In the header 19a of the last packet 19, the First-bit is 0 and the Last-bit is 1. In the header 18a of the packets 18 in between, both the First and Last bits are 0.
The internal construction of the data group 16 is of no importance with regard to packet switching, but it is of importance with regard to the invention, and so it is described in the following with reference to FIG. 4. At the beginning of the data group 16, there is a data group header 20, the length of which is 2 or 4 bytes, and thereafter possibly a session header 21, the length of which is not less than 3 and not more than 18 bytes, depending on the length of the address field 21f that may be contained in it. After that, there is a data group data field 22, the length of which is any integer number of bytes, but not more than 8191 bytes. The last one is a checksum field 23, if any, the length of which is 2 bytes. If the so called CRC flag bit 20b of the data group header 20 is 0, the data group 16 does not contain a checksum field.
The standard ETS 300 401 specifies how the bits of the data group header 20 are used to describe the contents of the data group 16. A part of the data group header 20, which is essential for the invention, is a four-bit code 20d indicating the type of the data group. If the four bits form the pattern 0011, data group 16 is of the file descriptor type, which is according to the above standard intended to describe the file to be transferred in the DAB system in order that the transfer would succeed. However, the standard does not specify the structure of a data group of the file descriptor type, and so file transfer in the DAB system is not defined merely on the basis of the existing standard.
Some procedures are known from other forms of digital data processing, in which procedures the nature of the data to be processed is described by headers or other auxiliary information. The patent specification U.S. Pat. No. 5,400,401 (Wasilewski et al; Scientific Atlanta Inc.) discloses a procedure in which data streams are transmitted as frames on the data transfer medium. For the transmission of the multiplexing order of the data streams, the system includes a multiplex control packet (or a virtual channel map packet), which describes the location of different services in the multiplexed stream. The purpose is that on the basis of information transmitted by this packet, the receiving device can pick the desired components from the data stream. The specification referred to does not describe the transfer of data in file form, but the transfer streams are essentially temporally continuous. The files essentially consist of the beginning, the middle part and the end, the identification of which is important in order to arrange the reception correctly.
The European patent applications EP 508 925 and EP 508 928 (IBM) disclose a method for transmitting multimedia data within a full-duplex data processing system. The system described by the applications is not of the broadcast service type, but it is constructed of local area networks and work-stations connected to them. The multimedia information can be of the stream or file type. The transfer forms include xe2x80x9cvideo frame dataxe2x80x9d, which can be considered to be of the stream type. In the IBM publications, the equivalent of a program is a xe2x80x9ctrackxe2x80x9d, and a table describing the track order is called a xe2x80x9ctrack collection indexxe2x80x9d. In the publications, attention is paid to the effect of different playback rates on the transfer of audio and video components of multimedia. It is proposed in those publications that the xe2x80x9csequence indexxe2x80x9d describing the order of the components must contain, in addition to information of the mutual order of the components, also information of the correct playback rate of the components. The full duplexity of the data transfer provides many possibilities that do not exist in broadcast-type distribution, and so the method presented by these reference publications cannot be as such applied to the systems to which the invention relates.
It is an object of this invention to present a method for the transfer of information in file form in a DAB system, which preferably complies with the standard ETS 300 401. Another object of the invention is to present a method for implementing a file descriptor data group type referred to in the above standard. Furthermore, it is an object of the invention to present a method for implementing the data group type so as to enable successful file transfer in a DAB system.
The objects of the invention are achieved by dividing the file to be transferred into segments, which are numbered by file-specifically consecutive numbers, by setting the bits of the data group header suitably and by adding to the data group data field parameters describing the file to be transferred, such as a parameter indicating the number of the segments. The setting of the header bits as well as the parameters and their values will be described in more detail below.
A method according to the invention for transmitting a file in a digital broadcasting system is characterized in that a data element describing the file to be transmitted is created in the method, which data element has the same form as the data group used in the broadcasting system, and the data element is transmitted in the broadcasting system from the transmitter to the receiver.
The invention also relates to transmitter and receiver equipment, which participate in the file transfer by means of the method according to the invention. Transmitter equipment according to the invention is characterized in that it comprises means for arranging information describing the file into a data group of a predetermined form. Receiver equipment according to the invention is characterized in that it comprises means for interpreting information describing the file from a data group of a predetermined form.
In the system according to the invention, the information contained by the file is divided into segments for the transfer, and the segments are numbered consecutively within each file and transmitted one at a time from the transmitter to the receiver. In a broadcasting system using the method according to the invention, data groups of the file descriptor type are used to transmit the information associated with the files, and the data groups are added to the DAB transmission in a manner known as such. When files are being transferred, the data group of the file descriptor type is added according to the invention temporally at least immediately before the first segment of the file to be transferred next. In addition, the file descriptor data group can be transmitted a good time before the transfer of the file associated with it begins. The file descriptor data group can also be added to the DAB transmission in the middle of the transfer of the file associated with it.